<IPv4 header>
| Feild | Description |
| Version | The version of IP.
* IPv4 : 0b0100
|
| IHL(IP Header Length) | Header length divided by 4.
* Generally 5.
|
| TOS(Type Of Service) | QoS related value. |
| Total Length | Header length + Data length. |
| Identification | The separator for identifying fragmented packets. When the packets with same identification are combined, they become the original data. |
| Flags (3 bits) | The option for fragmentation.
* X : reserved(100).
* D : Do not fragment(010).
* M : More fragments follow(001).
|
| Fragment ofsset (13 bits) | Fragmented packet's offset. |
| TTL(Time To Live) | Transmissible distance of a packet. |
| Protocol | The type of upper protocol.
* 01 : ICMP
* 02 : IGMP
* 06 : TCP
* 17 : UDP
|
| Header checksum | The checksum value for checking error of IPv4 header. |
| Source address Destination address | IPv4 address. |